Vehicle assist method

ABSTRACT

A control assist method for a vehicle including a power train connected to drive wheels by a clutch. The method updates a clutch curve which connects a position of a clutch pedal and a maximum torque that can be transmitted by the corresponding clutch, as a function of reliability thereof, the reliability being lower when the vehicle is first used and increasing with use of the vehicle.

BACKGROUND

The present invention relates to a power-assistance method for controlfor a vehicle having a manual or automatic gearbox, employing analgorithm for learning the clutch characteristic curve.

The invention relates in particular to power-assistance devices andmethods for uphill maneuvers, but it may also be applied to estimationof the wear of a vehicle clutch or even to control of an electronictrajectory control system (better known under the name ElectronicTraction Control, ETC) of a 4×4 vehicle.

On certain vehicles, the automobile manufacturers are offering apower-assisted parking brake.

By reason of its relatively high cost compared with the traditionalparking brake solution, this power-assisted parking brake must provideperformance that adds value for the customer.

To add value to this system, the manufacturers have therefore decided toassociate therewith a power-assistance function for uphill maneuvers andespecially power assistance for uphill starting (or pulling away),wherein the principle is to release the brakes on the non-driving wheelsas soon as the torque transmitted by the engine to the driving wheels issufficient to compensate for the inclination effect of the slope.

Such devices are already known.

In this regard, document GB 2376990 proposes a control module for apower-assisted parking brake device for a motor vehicle provided with amanual gearbox, which releases the force applied to the parking brakewhen it receives signals indicating to it, on the one hand, a positivedisplacement of the accelerator pedal and, on the other hand, that theposition of the clutch pedal has reached its bite point. The instant atwhich the device releases the brake also depends on the clutch-pedaldepression velocity, on the gear ratio engaged and on the slope on whichthe vehicle user is located.

This device has the disadvantage of being sensitive to the noise ofsensors, such as the inclination sensor. Furthermore, it takes only thebite point on the clutch characteristic curve into account. Thus it doesnot permit optimal pulling away on a steep slope.

Finally, another disadvantage of this method is that it is based oncalculation, from an estimate of the engine torque, of the torquetransmitted by the clutch corresponding to the bite point. Thus it doesnot take into account the aging of the clutch, and it is sensitive toactive consuming loads, such as the air-conditioning, the alternator orany other device consuming part of the energy supplied by the engine.

Document FR 2828450 in turn proposes a power-assistance method foruphill starting using the characteristics of the vehicle clutch by meansof an algorithm for estimating the torque transmitted to this clutch, inorder to control brake release more precisely during pulling away.

This estimate is made by plotting a clutch characteristic curve, whichgives the position and the maximum torque that can be transmitted by thecorresponding clutch. However, it is very sensitive to theinitialization of the said curve as well as to sensor noise.Furthermore, updating of the curve is slow and unsuitable for its degreeof reliability.

BRIEF SUMMARY

One objective of the invention is to propose a power-assistance method,especially for uphill maneuvers, which is insensitive to the activeconsuming loads.

Another objective of the invention is to propose a power-assistancemethod, especially for uphill maneuvers, which is based on an estimateof the clutch characteristic curve and which is not very sensitive toinitialization of the said clutch characteristic curve.

For that purpose, the invention proposes a power-assistance method,characterized in that it updates a clutch characteristic curve, the saidcurve linking the position of the clutch pedal and a maximum torque thatcan be transmitted by the corresponding clutch, as a function of itsreliability, its reliability being less at the start of use of thevehicle and increasing with use of the said vehicle.

Certain preferred but non-limitative aspects of the method according tothe invention are the following:

-   -   at least one of the following parameters is varied as a function        of the reliability of the curve:        -   a number of upshifts and/or downshifts taken into account            for each torque interval,        -   a threshold deviation,        -   a slipping threshold, or        -   a reliability factor,    -   the number of upshifts and/or downshifts, the threshold        deviation, the slipping threshold and/or the reliability factor        taken into account for the torque interval are parameterized as        a function of each torque interval,    -   the clutch characteristic curve is updated in real time        throughout the life of the vehicle,    -   it employs a power-assistance device according to the invention.

Finally, according to a last aspect of the invention, there is proposedthe employment of a power-assistance method according to the inventionin a vehicle, in order to aid a user of the vehicle to accomplish uphillmaneuvers, to estimate the wear of the vehicle clutch and/or to controlan electronic traction control system of a 4×4 vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics, objectives and advantages of the presentinvention will become apparent upon reading the detailed descriptionhereinafter with reference to the attached drawings, provided by way ofnon-limitative examples and wherein:

FIG. 1 presents the functional architecture of a vehicle equipped withthe device according to the invention,

FIG. 2 illustrates the functioning principle of the automatic systemthat estimates the torque transmitted to the wheels of a vehicleemployed in the invention,

FIG. 3 presents a discretization of the clutch characteristic curveaccording to the invention.

DETAILED DESCRIPTION

A vehicle equipped with a power-assistance device for uphill startingaccording to the invention comprises a motive power assembly, apower-assisted parking brake 5, a bus 4 on which the signals originatingfrom the rest of the vehicle 6 travel, and a computer for control of themotive power assembly.

Bus 4 is preferably a bus based on the CAN™ standard (Control AreaNetwork, meaning control zone network).

The motive power assembly is composed of a heat engine coupled to thedriving wheels by a transmission device provided with a gearbox and aclutch, controlled by the user or a computer depending on the type ofgearbox.

Alternatively, the motive power assembly may be provided with one ormore electrical machines, with or without heat engine.

The power-assistance device for uphill starting cooperates with acomputer 1 for control of power-assisted parking brake 5, which computeris also connected to bus 4.

Computer 1 is equipped in known manner with a means for producing ordersto apply and release power-assisted parking brake 5, the said orders 5being generated on a line for connection to power-assisted parking brake5 itself. If necessary, computer 1 is also equipped with a means fortransmitting to bus 4 items of information on the state ofpower-assisted parking brake 5.

Computer 1 for control of power-assisted parking brake 5 is connected byan appropriate line to an inclination sensor 2.

When the vehicle is stopped on a slope, inclination sensor 2 delivers asignal representative of the inclination of the slope on which thevehicle is stopped.

When computer 1 for control of power-assisted parking brake 5 producesan order to apply, the movable parts of the brakes cause the disks to beclamped in such a way that power-assisted parking brake 5 is applied.

Inversely, when computer 1 for control of power-assisted parking brake 5produces an order to release power-assisted parking brake 5, the movableparts of the brakes are released.

Furthermore, in the brake-release situation (regardless of theinclination of the slope), the motive power assembly of the vehicleproduces a torque, which is or is not transmitted to the wheels,depending on whether or not the clutch is active, and in a proportionthat depends on the clutch position.

Thus the device of the invention determines a condition for release ofpower-assisted parking brake 5, as a function in particular of theinclination of the slope and of the estimate of the torque ECTtransmitted to the clutch. This condition is determined in such a waythat the vehicle is capable of pulling away as soon as a certainthreshold, at which the slope effect is balanced by the engine torque,is exceeded.

In order to pull away, a vehicle parked on a slope must overcome theslope effect due to gravitational force.

This effect is a function of the inclination of the slope and of themass of the vehicle, and is equal tom·g·sin(θ_(slope))  (EQUATION 1)

where

-   -   m is the mass of the vehicle,    -   g is gravity,    -   θ_(slope) is the inclination of the slope.

The minimum torque C_(T) _(—) _(threshold) that must be transmitted tothe clutch via the kinematic chain of the wheel in order to permit thevehicle to pull away (or in other words to start on the slope) must beat least equal toC _(T) _(—) _(threshold) =ECT(θ_(clutch) _(—)_(threshold))=m·g·sin(θ_(slope))·r·(b)·ρ_(wheels)  (EQUATION 2)

where

-   -   r(b) is the engaged gearbox ratio corresponding to position b of        the gearshift lever,    -   ECT(θ_(clutch) _(—) _(threshold)) is the torque transmitted by        the clutch when the pedal is depressed to the position        θ_(clutch) _(—) _(threshold),    -   ρ_(wheels) is the radius under load of the vehicle wheels.

The torque C_(T) _(—) _(threshold) is in fact the pull-away thresholdtorque.

The strategy proposed by the invention is based on improving thealgorithm presented by the application FR 2828450, which proposes adevice making it possible to estimate the clutch characteristic curve(which, as we recall, links the position of the clutch pedal to themaximum torque applied by the clutch), in such a way that the device isless sensitive to wear and aging of the clutch as well as to the activeconsuming loads than are the methods based on calculation thereof. Thisalgorithm is illustrated in the attached FIG. 2 and will not bedescribed further. The associated method commands the release of thepower-assisted parking brake when the torque ECT transmitted to theclutch is greater than the pull-away torque C_(T) _(—) _(threshold)given by equation 2.

The difficulty consists in estimating the torque transmitted to theclutch as precisely as possible.

For that purpose, the algorithm and the method proposed by our inventionimprove blocks B and E of FIG. 2, namely the blocks for constructing theinput signals and for updating the clutch characteristic curve.

On the clutch characteristic curve, the bite point is defined ascorresponding to the pedal position for which the clutch begins totransmit a torque. This minimum torque may be, for example, on the orderof 3 N.m.

The bite point therefore corresponds to a clutch-pedal position at whichthe clutch is in a slipping phase.

This characteristic evolves with time, as a function of the wear of thelining of the friction plate of the clutch and of the flywheel of thevehicle, of the change, due to repeated use, in stiffness of the springsthat apply pressure to the clutch, etc.

The torque transmitted by the clutch is therefore determined on thebasis of a priori knowledge of the clutch characteristic curve. For thatpurpose, the clutch-pedal position at which the pull-away thresholdtorque C_(T) _(—) _(threshold) is transmitted must be determined bysolving equation 2. From this there is then deduced the positionθ_(clutch) _(—) _(threshold) that the clutch pedal must assume in orderto achieve a quality uphill start.

Since the clutch characteristic curve is sensitive to wear and aging ofthe clutch, it is necessary to update it throughout the entire life ofthe vehicle.

In the description hereinafter and in the attached figures we will usethe following notations to identify the mathematical variables involvedin the invention:

-   -   C_(m) _(—) _(CME) is the effective mean torque delivered by the        engine, estimated by the engine computer,    -   ω_(m) is the angular velocity of rotation of the engine,    -   ω_(R) is the angular velocity of rotation of the front wheels,    -   v is the longitudinal speed of the vehicle,    -   θ_(clutch) is the position of the clutch pedal,    -   θ_(acc) is the position of the accelerator pedal,    -   θ_(slope) is the inclination of the vehicle,    -   RE is the engaged gear ratio. RE=0 at the neutral point, and        RE=1 regardless of the engaged gear, except for reverse, in        which case RE=−1,    -   {dot over (x)} is the derivative of the variable x with respect        to time.

According to the invention, the clutch characteristic curve is estimatedon the basis of points acquired during phases of changing of the gearratio of the vehicle, preferably in the course of downshifts. In fact,during downshifts, the engine computer of the vehicle delivers a betterestimate of the engine torque C_(m) _(—) _(CME), since it must take intoaccount only the effect due to retraction of the pistons when they arein the air-intake phase, while during upshifts, the engine computer musttake into account the combustion temperature of the mixture, the amountof fuel actually injected, etc., thus making the estimate of the enginetorque C_(m) _(—) _(CME) much more complex and less certain.

Improvement of the Block for Constructing Signals Delivered by theSensors of the Vehicle:

The equations of the dynamic on which the method of the invention isbased are as follows:m{dot over (v)}=F _(x) −F _(res)J _(R)·{dot over (ω)}_(R) =C _(R)(θ_(clutch), ω_(m)−ω_(R))−ρ_(wheels) ·F_(x)J _(m)·{dot over (ω)}_(m) =C _(m) _(—) _(CME)(ω_(m), θ_(acc))−r(b)·C_(R)(θ_(clutch), ω_(m)−ω_(R))  EQUATION 3Thus:F _(x) =m·{dot over (v)}+F _(res)C _(R)(θ_(clutch), ω_(m)−ω_(R))=J _(R)·{dot over (ω)}_(R)−ρ_(wheels) ·F_(x)C _(m) _(—) _(CME)(ω_(m), θ_(acc))=J _(m)·{dot over (ω)}_(m) +r(b)·C_(R)(θ_(clutch), ω_(m)−ω_(R))  EQUATION 4

where

-   -   r(b)·C_(R)(θ_(slope), ω_(m)−ω_(R)) is the torque transmitted by        the clutch in the position θ_(clutch), which will be denoted        ECT(θ_(clutch))    -   F_(x) is the longitudinal component of the force of contact        between the vehicle wheel and the ground,    -   F_(res) is the longitudinal component of the resistance to        movement of the vehicle.

When slipping is sufficient, it is possible to use equation 4 toestimate the clutch characteristic curve. The following equations arethen obtained:ECT(θ_(clutch))=C _(m) _(—) _(CME) −J _(m){dot over (ω)}_(m)ω_(R) −r(b)·ω_(m)>Δω_(threshold)  EQUATION 5

The second equation is a condition on slipping. It indicates that thedifference between the angular velocity ω_(R) of the wheels and theangular velocity r(b)·ω_(m) of the clutch must be greater than athreshold angular velocity Δω_(threshold) in order to guarantee that thetorque transmitted by the clutch is the maximal torque that can betransmitted by the clutch at the position θ_(clutch) underconsideration.

To estimate the clutch characteristic curve, as can be shown by equation5, it is necessary that the variables C_(m) _(—) _(CME), θ_(clutch),ω_(m), ω_(R) and {dot over (ω)}_(m) be in phase.

Filtering and/or differentiation and/or delays are therefore applied tothe signals received at the input of block B, the said signalsoriginating from different sensors of the vehicle via the CAN bus, toensure that the signals at the output of block B will be in phase.

The sensors may be, for example, an inclination sensor, a clutch sensor,a sensor of the angular velocity of rotation of the engine, etc.

For that purpose, the device of the application uses FIR filters (forFinite Impulse Response, or finite response to impulses). When itreceives an input signal arriving from a sensor, it introduces a delayinto the said signal for the purpose of reducing the noise of thecorresponding sensor, in a manner known in itself. The output signaly(t) of an FIR filter for an input signal x(t) is therefore:

$\begin{matrix}{{y(t)} = {\sum\limits_{i = 1}^{N}{a_{i} \cdot {x\left( {t - {i \cdot T}} \right)}}}} & {{EQUATION}\mspace{14mu} 6}\end{matrix}$

where

-   -   a_(i) is the i-th coefficient of the FIR filter,    -   N is the total number of coefficients of the FIR filter,    -   x(t−i·T) is the input signal of the filter delayed by i·T        seconds.

The device according to the invention may additionally be provided withfilters for differentiation over m samples, which introduce a delay alsoknown in itself (of the m/2 type).

For example, such filters may be constructed according to the followingequation:

$\begin{matrix}{{y(t)} = \frac{{\sum\limits_{k = 1}^{m}{x(k)}} - {x\left( {k - m} \right)}}{m \cdot {Ts}}} & {{EQUATION}\mspace{14mu} 7}\end{matrix}$

where

-   -   Ts is the sampling time.

It is also possible to introduce constant delays in order to alleviatethe delays due, for example, to filtering operations, to differentiationoperations (especially in the course of the operation in which ω_(m) isdifferentiated in order to obtain {dot over (ω)}_(m)) or to differentsampling intervals on the CAN bus. The output signal y(t) is thenexpressed as having a constant delay relative to an input signal x(t)such thaty(t)=x(t−T)  EQUATION 8

where

-   -   x(t−T) is the input signal delayed by T seconds.

Finally, variable delays may be introduced, these delays being linked tothe characteristics of certain sensors.

For example, the engine speed sensor delivers an item of information onthe speed of rotation of the engine in revolutions per minute: dependingon the speed of rotation of the engine, the item of information isdelivered more or less frequently, since it is obtained at the moment atwhich the engine executes a complete revolution. Thus the other signals,such as the estimate of the engine torque C_(m) _(—) _(CME), must bebrought into phase with the instant of delivery of this engine signalω_(m). The output signal y(t) is then expressed as having a variabledelay relative to an input signal x(t) such that:

$\begin{matrix}{{y(t)} = \left\{ \begin{matrix}{x(t)} & {{{if}\mspace{14mu}\omega_{m}^{0}} \leq {\omega_{m}(t)} < \omega_{m}^{1}} \\{x\left( {t - T} \right)} & {{{if}\mspace{14mu}\omega_{m}^{1}} \leq {\omega_{m}(t)} < \omega_{m}^{2}} \\\ldots & {{if}\mspace{14mu}\ldots} \\{x\left( {t - {\left( {i - 1} \right) \cdot T}} \right)} & {{{if}\mspace{14mu}\omega_{m}^{i - 1}} \leq {\omega_{m}(t)} < \omega_{m}^{i}} \\{x\left( {t - {i \cdot T}} \right)} & {{{if}\mspace{14mu}{\omega_{m}(t)}} \geq \omega_{m}^{i}}\end{matrix} \right.} & {{EQUATION}\mspace{14mu} 9}\end{matrix}$

where

-   -   ω_(m) ^(i) is the i-th angular velocity threshold of the engine,    -   x(t−iT) is the input signal delayed by i·T seconds.

The use of these filters on the input signals therefore makes itpossible to increase the robustness to noise of the sensors of thealgorithm used by the device of the Application, by taking into accountthe delays due to the use of certain parameters during estimation of theclutch characteristic curve.

Improvement of Updating of the Clutch Characteristic Curve

In order to obtain the clutch characteristic curve, points CC(θ_(clutch)_(—) _(CC), ECT_(CC)) relating the position θ_(clutch) of the clutchpedal and the maximal torque ECT that can be transmitted by the clutchare measured then recorded. The clutch characteristic curve is thendiscretized into N_(intervals) intervals of torque ECT, as illustratedin the attached FIG. 3, each interval i (1≦i≦N_(intervals)) beingassociated with a point CC_(i)(θ_(clutch) _(—) _(CC)(i), ECT_(CC)(i)).

Preferably the intervals i (1≦i≦N_(intervals)) are regular intervals,bounded by the torques ECT_(Min)(i) and ECT_(Max)(i) transmitted by theclutch, with ECT_(Max)(i)=ECT_(Min)(i=1) (for 1≦N_(intervals)−1).

Any other discretization may be envisioned, such as that represented inFIG. 3. Nevertheless, finer discretization is preferable for smallvalues of ECT, to ensure that the clutch characteristic curve will bemore precise around the bite point.

Preferably the signals taken into account for construction of the clutchcharacteristic curve are the signals obtained at the output of block B,namely signals filtered to make them robust to sensor noise and/orretarded to bring them into phase.

The algorithm and the method according to the invention comprise thefollowing steps:

In the course of a first step, if a change of gear ratio is detected, acommand to store points ({tilde over (θ)}_(clutch), E{tilde over (C)}T,{tilde over (ω)}_(R), {tilde over (ω)}_(m)) in memory is generated, inorder that the items of information about the clutch-pedal positionθ_(clutch), the engine speed of rotation ω_(m), the speed of rotation ofthe wheels ω_(R) and the torque ECT transmitted by the clutch will beentered in memory in a recording means. During a return shift, amultitude of points ({tilde over (θ)}_(clutch), E{tilde over (C)}T,{tilde over (ω)}_(R), {tilde over (ω)}_(m)) is captured in this way.

In the course of a second step, the method determines whether a gearratio has been engaged and, if so, whether the gear change is adownshift. If this condition is not satisfied, the method does not takethe captured points into account and rejects them. Otherwise itprogresses to a third step, in the course of which it analyzes thecaptured points.

Of course, as we have seen hereinabove, the return-shift condition is arestriction chosen only to increase the robustness of the algorithmassociated with the method. If the estimate of the engine torque isjudged to be sufficiently reliable, this restriction may be canceled, insuch a way that the points stored in memory during an upshift are alsotaken into account.

During the analysis of the captured points ({tilde over (θ)}_(clutch),E{tilde over (C)}T, {tilde over (ω)}_(R), {tilde over (ω)}_(m)) in thecourse of the third step, the method establishes, for each point,whether it falls within an interval i of the clutch characteristiccurve. If so, the point is then entered into memory. Otherwise the pointis rejected.

Using the notation:

-   -   {tilde over (x)} for the item of information captured for the        variable x,    -   x for the mean calculated over the variable x,    -   {tilde over (P)}_(i,j) ({tilde over (θ)}_(clutch) (i), E{tilde        over (C)}T (i)) for the j-th point captured in the course of a        return shift to the i-th interval of the clutch characteristic        curve,        the conditions that such a point ({tilde over (θ)}_(clutch),        E{tilde over (C)}T, {tilde over (ω)}_(R), {tilde over (ω)}_(m))        must satisfy to be entered into memory by the device are as        follows:    -   the point must fall within the interval i: ECT_(Min) (i)<E{tilde        over (C)}T<ECT_(Max) (i)    -   the slipping must be greater than a given threshold        Δω_(threshold): Δω={tilde over (ω)}_(R)−{tilde over        (ω)}_(m)·r(b)>Δω_(threshold)    -   the deviation between the captured point and the point of the        clutch characteristic curve to be updated in the interval i        (θ_(clutch) _(—) _(CC)(i) must be small, for example smaller        than a threshold Δθ_(clutch): |{tilde over        (θ)}_(clutch)−θ_(clutch) _(—) _(CC)(i)|<Δθ_(clutch).

In the course of a fourth step, executed every n_(re-clutch) returnshifts, the acquired n_(i) points of an interval i are averaged andentered into memory for each interval (in other words for i between 1and N_(intervals)), in order to filter the errors due to modeling and tocapture of the measurements:

${\overset{\_}{P}}_{i} = \frac{\sum\limits_{j}{\overset{\_}{P}}_{ij}}{n_{i}}$

where

-   -   P _(i)= P _(i) ( θ _(clutch) (i), E CT (i)) is the mean of the        points captured in the i-th interval of the clutch        characteristic curve.

Thus the clutch characteristic curve is itself determined following thecapture and averaging of a set of points obtained in the course of anumber n_(re-clutch) of return shifts (or even in the course of a numbern_(re-clutch) of upshifts and/or downshifts).

The first three steps are executed in all return shifts (or even in allthe upshifts and/or downshifts), while the fourth and fifth steps (seehereinafter) are executed only every n_(re) _(—) _(clutch) return shifts(or even every n_(re) _(—) _(clutch) upshifts or downshifts).

Furthermore, the number n_(re-clutch) of return shifts taken intoaccount as well as the error Δθ_(clutch) between the captured point{tilde over (θ)}_(clutch) and the point θ_(clutch) of the clutchcharacteristic curve may vary as a function of the reliability of theclutch characteristic curve. Thus, to increase the robustness of thealgorithm and of the method according to the invention, these twoparameters may be varied in the course of the life of the vehicle (andof its use).

For example, at the beginning of life of the vehicle, when the vehiclehas experienced little use, when the clutch characteristic curve is lessreliable, or in other words during the first return shifts executed onthe vehicle or during the first kilometers traveled by the vehicle, thevalue of the number n_(re-clutch) of return shifts taken into account inaveraging and the value Δθ_(clutch) of the error threshold for a giveninterval i can be fixed at a high value, in such a way that all capturedpoints are accepted and the error due to the measurements and to themodeling are finely filtered in the course of the method. Suchparameterization therefore makes it possible to improve theinitialization of the clutch characteristic curve appreciably.

Subsequently, in the course of use of the vehicle, the value attributedto these two parameters may then be reduced, since the clutchcharacteristic curve obtained and entered into memory according to theinvention tends to converge toward the real clutch characteristic curve.

Finally, in the course of a fifth step, the method determines the updateof the clutch characteristic curve, which preferably is carried out bymeans of a first-order low-pass filter, applied to each of the torqueintervals (11≦i≦N_(intervals)) every n_(re-clutch) return shifts:CC _(i)(k)=α_(clutch) _(—) _(curve) ·CC _(i)(k−1)+(1−α_(clutch) _(—)_(curve))· P _(i)(k)  EQUATION 10

where

-   -   α_(clutch) _(—) _(curve) is a reliability factor,    -   k indicates the calculation interval (every n_(re-clutch) return        shifts).        -   Thus CC_(i)(k) is the point of the clutch characteristic            curve in the torque interval i at the calculation interval k            (or in other words after k*n_(re-clutch) return shifts).        -   CC_(i)(k−1) is the point of the clutch characteristic curve            in the torque interval i at the calculation interval (k−1)            (or in other words after (k−1)*n_(re-clutch) return shifts).        -   P _(i)(k) is the mean of the points captured between the            k*n_(re-clutch) return shifts and the (k−1)*n_(re-clutch)            return shifts.

A value between 0 and 1 is attributed to the reliability coefficientα_(clutch) _(—) _(curve) as a function of the reliability of the clutchcharacteristic curve.

Thus, for a reliable curve, the reliability coefficient α_(clutch) _(—)_(curve) will be closer to 1 than for a poorly reliable clutchcharacteristic curve, for which the reliability coefficient will beclose to zero.

This parameter α_(clutch) _(—) _(curve) can itself be parameterized and,just as the value of the number n_(re-clutch) of return shifts takeninto account in averaging and the value Δθ_(clutch) of the errorthreshold, it may vary in the course of the vehicle life, in order thatthe curve obtained by the algorithm according to the invention willconverge more rapidly toward the real clutch characteristic curve.

For example, during the first return shifts or during the firstkilometers traveled by the vehicle, the value of α_(clutch) _(—)_(curve) may be chosen to be low (close to zero) and then increasedprogressively as time passes. The weight of the most recently recordedpoint CC_(i)(k−1) will therefore be less than that of the mean point P_(i)(k) for the value attributed to the point CC_(i)(k).

In this way updating and learning of the clutch characteristic curve ofthe vehicle in real time throughout the entire life thereof isguaranteed.

The invention claimed is:
 1. A power-assistance method for control by acomputer of a vehicle provided with a motive power assembly connected todriving wheels by a clutch, comprising: detecting, by the computer, achange of a gear ratio and, when the change of the gear ratio isdetected, storing points related to a clutch pedal position, an enginespeed of rotation, a speed of rotation of the wheels, and a torquetransmitted by the clutch; determining, by the computer, whether each ofthe stored points falls within one of a plurality of intervals of aclutch characteristic curve; for each interval of the plurality ofintervals, averaging, by the computer, the stored points determined tofall into the interval to determine an average value of the storedpoints and storing the average value in a memory; determining, by thecomputer, a reliability coefficient that is a function of a reliabilityof the clutch characteristic curve, the reliability coefficient being alower value at a start of use of the vehicle and increasing with use ofthe vehicle; updating, by the computer, the clutch characteristic curveaccording to the following equation:CC _(i)(k)=α_(clutch) _(—) _(curve) ·CC _(i)(k−1)+(1−α_(clutch) _(—)_(curve))·P _(i)(k), where CC_(i)(k) is an updated value of a point ofthe clutch characteristic curve at the interval i at a calculationinterval k, α_(clutch) _(—) _(curve) is the reliability coefficient,CC_(i)(k−1) is the current value of a point of the clutch characteristiccurve at the interval i at a calculation interval k−1, and P_(i)(k) isthe average value of the stored points for the interval i, the clutchcharacteristic curve linking a position of a clutch pedal and a maximaltorque that can be transmitted by the corresponding clutch; determining,by the computer, a torque transmitted by the clutch according to theupdated clutch characteristic curve; and releasing, by the computer, abrake of the vehicle when the torque transmitted by the clutch exceeds atorque required for the vehicle to pull away.
 2. A power-assistancemethod according to claim 1, wherein the clutch characteristic curve isupdated in real time throughout a life of the vehicle.
 3. Apower-assistance method according to claim 1, employing apower-assistance device.
 4. A power-assistance method according to claim1, wherein the determining whether each of the stored points fallswithin one of a plurality of intervals of a clutch characteristic curveincludes rejecting the stored points that are not determined to fallwithin one of the intervals.
 5. A power-assistance method according toclaim 1, wherein the detecting includes rejecting the stored points whenthe gear change is not a downshift.
 6. A power-assistance methodaccording to claim 1, wherein the reliability coefficient increases from0 to 1 with the use of the vehicle.